Field of the Invention
The present invention relates to a sheet conveyance apparatus conveying a sheet and more specifically to a configuration of a bearing supporting a shaft portion of a conveyance roller.
Description of the Related Art
Conventionally, a sheet conveyance apparatus applicable to an image forming apparatus such as a copier, a printer, a multi-function printer including copying and printing functions, and a facsimile and to an image reading apparatus includes a conveyance roller for delivering a sheet in a sheet conveying direction. Lately, the conveyance roller is often made of an inexpensive material and formed into a small size because it is demanded to downsize and to cut a cost of an entire apparatus.
If rigidity of a roller shaft of the conveyance roller drops by downsizing the conveyance roller, there is a possibility that the roller shaft deflects in a case when a relatively large pressure acts on the conveyance roller or on an approximately center part thereof in particular due to a pinch pressure caused with a conveyance driven roller opposing the conveyance roller. In order to prevent such deflection of the roller shaft, there is known a sheet conveyance apparatus including a conveyance roller in which two or more roller portions are provided around one roller shaft and supporting the roller shaft at three places of both end parts and a center part of the roller shaft to a frame by bearings as disclosed in Japanese Patent Application No. 2002-284389 for example. According to this sheet conveyance apparatus, it is possible to prevent the deflection of the roller shaft because the roller shaft is supported by the bearing also at the center part. It is noted that the roller shaft and the bearings of the conveyance roller are disposed basically coaxially. Each bearing is supported by the frame and supports the roller shaft rotatably with respect to the frame and immovably in a direction orthogonal to an axial direction.
However, because each bearing supports the roller shaft with respect to the frame immovably in the direction orthogonal to the axial direction in the sheet conveyance apparatus described above, there is a possibility of causing the following problems. That is, there is a case when the roller shaft of the conveyance roller has warpage and torsion in a longitudinal direction due to a variation of component accuracy. In this case, there is a possibility that the roller shaft is attached to the bearing coaxially disposed in an eccentric condition in which a center of the shaft is minutely deviated. If the conveyance roller is rotationally driven in the eccentric condition, rotational resistance and driving torque increase. Still further, there is a possibility of causing uneven slidability between the roller shaft and the bearing. If the driving torque increases, there is a possibility of needing to increase an output torque or size of a driving motor. Still further, if the uneven slidability is generated, there is a possibility of dropping sheet conveyance accuracy or of generating abnormal noise.